The present invention relates to disc drive data storage systems and, more particularly, to a disc drive data storage system having a slider, which reduces stiction with the disc surface while providing sufficient bearing stiffness.
Disc drives of the xe2x80x9cWinchesterxe2x80x9d and optical types are well known in the industry. Such drives use rigid discs, which are coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor, which causes the discs to spin and the surfaces of the discs to pass under respective hydrodynamic (e.g. air) bearing disc head sliders. The sliders carry transducers, which write information to and read information from the disc surfaces.
An actuator mechanism moves the sliders from track-to-track across the surfaces of the discs under control of electronic circuitry. The actuator mechanism includes a track accessing arm and a suspension for each head gimbal assembly. The suspension includes a load beam and a gimbal. The load beam provides a load force which forces the slider toward the disc surface. The gimbal is positioned between the slider and the load beam, or is integrated in the load beam, to provide a resilient connection that allows the slider to pitch and roll while following the topography of the disc.
The slider includes a bearing surface, which faces the disc surface. As the disc rotates, the disc drags air under the slider and along the bearing surface in a direction approximately parallel to the tangential velocity of the disc. As the air passes beneath the bearing surface, air compression along the air flow path causes the air pressure between the disc and the bearing surface to increase, which creates a hydrodynamic lifting force that counteracts the load force and causes the slider to lift and fly above or in close proximity to the disc surface.
One type of slider is a xe2x80x9cself-loadingxe2x80x9d air bearing slider, which includes a leading taper (or stepped-taper), a pair of raised side rails, a cavity dam and a subambient pressure cavity. The leading taper is typically lapped or etched onto the end of the slider that is opposite to the recording head. The leading taper pressurizes the air as the air is dragged under the slider by the disc surface. An additional effect of the leading taper is that the pressure distribution under the slider has a first peak near the taper end or xe2x80x9cleading edgexe2x80x9d due to a high compression angle of the taper or step, and a second peak near the recording end or xe2x80x9ctrailing edgexe2x80x9d due to a low bearing clearance for efficient magnetic recording. This dual-peak pressure distribution results in a bearing with a high pitch stiffness.
The bearing clearance between the slider and the disc surface at the recording head is an important parameter to disc drive performance. As average flying heights continue to be reduced, it is important to control several metrics of flying height performance, such as flying height sensitivity to process variations, ambient pressure (e.g., altitude) variations, changes in radial position of the slider over the disc surface and resulting head skew, and quick movements of the slider from one radial position to another radial position.
The above-mentioned sensitivities are reduced by providing the slider with a high bearing stiffness in the pitch and roll directions. To achieve high pitch and roll stiffness, air bearings have utilized geometries that distribute the positive pressure away from the center of the slider. However, with some bearing geometries, it is difficult to generate sufficient localized pressure along certain areas of the bearing surface. For example, it is difficult to generate localized positive pressure near the trailing edge of a slider having truncated side rails and a discrete center pad positioned at the trailing edge.
Also, the slider should take off from the disc surface as quickly as possible after the start of disc rotation. Therefore, it is desired to limit the sticking friction (xe2x80x9cstictionxe2x80x9d) between the slider and the disc surface during the start and stop of disc rotation. One method of limiting stiction is to provide the disc surface with a textured landing zone, which reduces the contact area between the slider and the disc surface when the slider is at rest within the landing zone. However, as the flying heights are reduced to achieve higher recording densities, it becomes more difficult to implement a textured landing zone since the flying height can become less than the height of the roughness peaks that is required to limit the stiction forces in the textured landing zone.
This difficulty has lead to the use of head-disc interfaces in which some of the landing zone roughness is transferred to the bearing surface of the slider body. A textured bearing surface is typically achieved by forming discrete pads on the bearing surfaces. These pads provide small surface areas for contacting the disc surface without significantly effecting the bearing characteristics.
However, the use of textured bearing surfaces makes it more difficult to maintain the desired spacing between the head and the disc within the smooth data zone due to the additional separation caused by the pads. The head is typically positioned along the trailing edge of the slider body. In order to prevent the pads from interfering with the head-to-disc spacing, the pads are typically positioned somewhat forward from the trailing edge. This will allow the head to remain at the close-point flying height when the slider flies with a positive pitch angle. If the pads are positioned only a moderate distance from the trailing edge, the slider must fly with a relatively high pitch angle to maintain the desired head-to-media separation. A higher pitch angle decreases the bearing stiffness, and is typically detrimental to manufacturing sensitivity. If the pads are positioned at a large distance from the trailing edge, there will be a relatively large area on the bearing surface that has no pads. This can cause the slider to tip backwards if the disc oscillates backward and forward slightly during shut-down as the remaining energy in the disc and spindle motor coils dissipates. Backward tipping induces contact between the trailing edge of the slider and the disc surface, which can result in a disc lube meniscus being formed at the area of contact and an unacceptable stiction force if the disc surface is too smooth.
A slider is desired, which minimizes stiction with the disc surface while maintaining a low head-disc spacing and high bearing stiffness properties.
One aspect of the present invention relates to a disc head slider, which, includes a cavity dam, a subambient pressure cavity and first and second elongated rails. The subambient pressure cavity trails the cavity dam and has a cavity floor. The first and second rails are disposed about the subambient pressure cavity. Each of the rails has a rail width measured from an inner rail edge to an outer rail edge, a leading bearing surface, a trailing bearing surface, and a recessed area extending between the leading and trailing bearing surfaces. The recessed area is recessed from the bearing surfaces and raised from the cavity floor, across the rail width. First and second convergent channels are recessed within the trailing bearing surfaces of the first and second rails, respectively. Each channel has a leading channel end open to fluid flow from the respective recessed area, non-divergent channel side walls and a trailing channel end closed to the fluid flow and forward of a localized region of the respective trailing bearing surface.
Another aspect of the present invention relates to a disc drive assembly, which includes a housing, a disc, an actuator and a slider. The disc is rotatable about a central axis within the housing and has a recording surface with a data area and a landing area, which are non-textured. The actuator is mounted within the housing. The slider is supported over the recording surface by the actuator and includes a cavity dam, a subambient pressure cavity and first and second elongated rails. The subambient pressure cavity trails the cavity dam and has a cavity floor. The first and second rails are disposed about the subambient pressure cavity. Each of the rails has a rail width measured from an inner rail edge to an outer rail edge, a leading bearing surface, a trailing bearing surface, and a recessed area extending between the leading and trailing bearing surfaces. The recessed area is recessed from the bearing surfaces and raised from the cavity floor, across the rail width. First and second convergent channels are recessed within the trailing bearing surfaces of the first and second rails, respectively. Each channel has a leading channel end open to fluid flow from the respective recessed area, non-divergent channel side walls and a trailing channel end closed to the fluid flow and forward of a localized region of the respective trailing bearing surface.
Yet another aspect of the present invention relates to a disc drive assembly, which includes a disc and a slider. The disc is rotatable about a central axis and has a data area and a slider landing area, which are non-textured. The slider is supported over the disc and has elongated rails with convergent channels and recessed waist areas for generating a fluid bearing between the slider and the disc as the disc rotates beneath the slider about the central axis and for reducing stiction between the slider and the disc when the slider is at rest within the landing zone.